In a digitally controlled inkjet printing system, a receiver media (also referred to as a print medium) is conveyed past a series of components. The receiver media can be a cut sheet of receiver media or a continuous web of receiver media. A web or cut sheet transport system physically moves the receiver media through the printing system. As the receiver media moves through the printing system, liquid (e.g., ink) is applied to the receiver media by one or more printheads through a process commonly referred to as jetting of the liquid. The jetting of liquid onto the receiver media introduces significant moisture content to the receiver media, particularly when the system is used to print multiple colors on a receiver media. Due to the added moisture content, an absorbent receiver media expands and contracts in a non-isotropic manner, often with significant hysteresis. The continual change of dimensional characteristics of the receiver media can adversely affect image quality. Although drying is used to remove moisture from the receiver media, drying can also cause changes in the dimensional characteristics of the receiver media that can also adversely affect image quality.
FIG. 1 illustrates a type of distortion of a receiver media 3 that can occur during an inkjet printing process. As the receiver media 3 absorbs the water-based inks applied to it, the receiver media 3 tends to expand. The receiver media 3 is advanced through the system in an in-track direction 4. The perpendicular direction, within the plane of the un-deformed receiver media, is commonly referred to as the cross-track direction 7. Typically, as the receiver media 3 expands (or contracts) in the cross-track direction 7, contact between the receiver media 3 and contact surface 8 of rollers 2 (or other web guiding components) in the inkjet printing system can produce sufficient friction such that the receiver media 3 is not free to slide in the cross-track direction 7. This can result in localized buckling of the receiver media 3 away from the rollers 2 to create lengthwise flutes 5, also called ripples or wrinkles, in the receiver media 3. Wrinkling of the receiver media 3 during the printing process can lead to permanent creases in the receiver media 3 which adversely affects image quality.
U.S. Pat. No. 5,611,275 to Iijima et al., entitled “Width adjusting device and method for a paper web,” describes a device for adjusting the width of a paper web travelling through a print. The paper web is sandwiched between a pair of rollers having a plurality of contact surfaces which are arranged in an interleaved pattern. As the rollers are moved toward each other, the paper web is subjected to contacting pressure and is deformed to form a wavy surface, thereby decreasing the primary width of the paper web.
U.S. Patent Application Publication 2010/0054826 to Hieda, entitled “Web transfer method and apparatus,” discloses a web control system that includes a tiered roller and a pair of nip rollers. The tiered roller is formed to have a larger diameter at both ends than in a central portion. The nip rollers are arranged to incline outward to spread the web as it passes between the tiered roller and the nip rollers.
There remains a need for a means to prevent the formation of receiver media wrinkles as a receiver media contacts web-guiding structures in a digital printing system.